i will do Cube mod with a Asus ProGaming Aura.
The motherboard will be mountet on the handlemechanism with custom standoffs.
Are there some measurement for the cutout for Ioshield allready. Do i have to modify the Ioshield?

You'll probably have to cut the left side of the shield a little bit so that it will fit, but it will be close. Unfortunately, you'll probably just have to do your own measurements- all of these cube builds are unique in their own way, so it's best to look at how yours will fit exactly.